Millimeter wave signals are used for radar and telecommunications. They are also capable of being used to produce data representative of a subject by directing millimeter-wave signals at the subject and detecting the reflected signal. Examples of such imaging systems have been described in U.S. Pat. Nos. 5,455,590; 5,557,283; 5,859,609; and 6,507,309; and U.S. patent application No. 10/607,552 filed Jun. 26, 2003 (issued as U.S. Pat. No. 6,872,322 on Apr. 5, 2005); U.S. patent application No. 10/697,848 filed Oct. 30, 2003; U.S. patent application No. 10/301,552 filed Nov. 21, 2002 (issued as U.S. Pat. No. 6,703,964 on Mar. 9, 2004); and U.S. patent application No. 10/697,965 filed Oct. 30, 2003, which patent references are incorporated herein by reference.